Many debilitating human diseases are associated with the extracellular misfolding and aggregation of globular proteins to form fibrillar deposits that are rich in ?-sheet. There is considerable evidence that the process is initiated by local unfolding of the native structure to form aggregation-prone amyloidogenic intermediates. Aggregation then proceeds via nucleation-growth or downhill polymerization mechanisms. Despite their key role in amyloidogenesis, influencing the kinetic partitioning between aggregation and refolding pathways, very little is known about the structure of amyloidogenic intermediates because of their strong propensity to aggregate. The goals of the present proposal are to apply state-of-the-art NMR methods to elucidate the fundamental molecular events involved in initiation of transthyretin amyloidogenesis. Transthyretin amyloidosis is associated with numerous neurodegenerative diseases and cardiomyopathies. Misfolding and aggregation of transthyretin leads to fibrous deposits in the peripheral nerves and heart. Deposition of wild type protein is age related, whereas the familial diseases associated with genetic mutations that destabilize the quaternary and/or tertiary structure are early onset. This research will provide novel insights into the fundamental molecular mechanisms by which familial mutations destabilize the native transthyretin tetramer and initiate the aggregation cascade. Recently developed NMR relaxation dispersion experiments will be utilized to elucidate the structure of an aggregation-prone, early amyloidogenic intermediate and determine the kinetics and thermodynamics of the processes by which it is formed by partial unfolding of the monomeric transthyretin subunit.